CN106835127A - A kind of forced cooling device for laser melting coating directional solidificating alloy - Google Patents

Abstract

A forced cooling device for laser cladding directionally solidified alloys proposed by the present invention belongs to the technical field of laser forming and repairing of turbine blades of aeroengines, and includes the upper part of the forced cooling device and the lower part of the forced cooling device, and the upper and lower parts are connected by threads , a gasket is installed at the joint; wherein, the upper part of the forced cooling device includes an upper body and a heat dissipation structure located at the bottom center of the upper body, and a workpiece groove matching the size of the workpiece is opened in the center of the upper body, and the upper body is evenly provided for installation. The pressure plate and the threaded hole connecting the lower part of the forced cooling device; the center of the upper surface of the lower part of the forced cooling device is provided with a cooling water channel matching the size of the heat dissipation structure. Export. The invention has the advantages of simple manufacture, safe operation and low cost, can increase the temperature gradient of the front edge of the solidification interface, and contributes to the epitaxial growth of the superalloy directional solidification structure.

Description

A forced cooling device for laser cladding directionally solidified alloy

technical field

The invention belongs to the technical field of laser forming and repairing of aeroengine turbine blades, and in particular relates to a forced cooling device for laser cladding directional solidification alloy.

Background technique

The aero engine is called the heart of the aircraft and provides power for flight. It can be said that the power and stability of the engine are largely a standard for evaluating the performance of the aircraft, and the turbine blades of the aero engine are the guarantee of the engine performance. At present, advanced aero-engines place high demands on the ability of turbine blades to work under high temperature and high pressure.

In order to adapt to the working environment of high temperature and high pressure, the turbine blades located at the hot end of the aero-engine mostly use nickel-based directionally solidified superalloys. The manufacturing cost of nickel-based directionally solidified superalloy turbine blades is very high. Since the blades have been served in high-temperature and high-pressure environments for a long time, damages such as cracks and wear often occur. At present, laser cladding is mostly used to repair the damage of nickel-based directionally solidified superalloy blades. Laser cladding technology was developed in the 1970s. Its basic principle is to use laser as a heat source to sinter the cladding material to the thin layer on the surface of the substrate, so that the cladding material and the substrate are metallurgically combined to form a cladding layer. Due to the concentration of laser energy, the interaction time with the surface of the substrate is short during the process, so it has the advantages of small heat-affected zone, small thermal deformation, and low dilution rate. In order to meet the current repair requirements of directionally solidified superalloy blades, the repair structure needs to grow epitaxially and directionally on the basis of the growth direction of the original substrate structure to form a directionally solidified structure. Scholars at home and abroad have found that the growth of directional solidified structures depends on the ratio (G/V) of the temperature gradient (G) at the front of the solidification interface to the solidification rate (V). When G/V is greater than a certain critical value (the critical value is related to the alloy composition), the directionally solidified structure is a directionally grown columnar grain. Therefore, increasing the temperature gradient at the front of the solidification interface during laser cladding is conducive to the growth of directional solidified structures, and obtaining directional solidified structures with a larger volume fraction is of great significance for the repair of superalloy turbine blades.

Adjusting the laser process parameters can change the temperature gradient at the front of the solidification interface to a certain extent. In addition, adding certain cooling measures during the laser cladding process can also effectively increase the temperature gradient.

He Bin of Xi'an Jiaotong University, etc., used a liquid argon cooling device to assist in changing the temperature gradient at the front of the solidification interface during the solidification process during the laser deposition forming process of the substrate. The overall structure of the device is shown in Figure 1. The device consists of a liquid argon delivery pipe 01, a liquid argon storage tank 02, a connecting piece 04 and a liquid argon nozzle 05, and the connecting piece 04 is used to respectively install and fix the two liquid argon nozzles 05 on On both sides of the laser head 03, the liquid argon nozzle 05 and the liquid argon storage tank 02 are connected with the liquid argon delivery pipe 01. 06 is the deposition layer, and 07 is the width section of the substrate. When working, laser deposition is carried out along the length direction of the substrate, and then the laser is stopped. Liquid argon is sprayed through the liquid argon nozzle to cool both sides of the metal deposited part, and then the cooling is stopped for laser deposition. The deposition, laser deposition process and cooling process are carried out alternately until the preset height of the deposition layer 06 is reached and then stopped. Continuous columnar crystals can be obtained by using this cooling device, but there are two problems: one is that the cooling is applied on both sides of the deposition layer, which causes the growth direction of the columnar crystals to be biased towards the two walls where the cooling is applied, rather than vertically upward epitaxial growth; Laser deposition and cooling are carried out alternately, and the deposition rate is low.

Zhang Yaocheng of Shanghai Jiaotong University and others used a liquid nitrogen cooling device in the process of laser cladding nickel-based superalloys. The overall structure of the device is shown in Figure 2. The device consists of liquid nitrogen container 004, liquid nitrogen 005 and substrate support 006 composition. The substrate support is supported on the bottom of the container, the substrate 003 is placed on the substrate support 006, and the part below the surface of the substrate is immersed in a container filled with liquid nitrogen, and the laser 001 is turned on for laser cladding to form a cladding layer 003 . Although the use of liquid nitrogen cooling can increase the temperature gradient (G) at the front of the solidification interface during the cladding process, but because the drastic cooling effect on the overall workpiece will increase the solidification rate (V) to a greater extent, it will inhibit the formation of directional solidification structures, so The formed structure is mostly fine and non-directional equiaxed grain structure. This device is suitable for laser cladding of superalloys that do not require the formation of directional solidification structures, and cannot promote the formation of directional solidification structures.

Contents of the invention

The object of the present invention is to provide a forced cooling device for laser cladding directionally solidified alloy in order to overcome the deficiencies of the prior art. The device of the invention can quickly reduce the temperature at the bottom of the workpiece during the laser cladding process, increase the temperature gradient at the front of the solidification interface, and obtain a directionally solidified columnar crystal structure with consistent direction and larger volume fraction in the experimental test.

The invention proposes a forced cooling device for laser cladding directionally solidified alloys, which is suitable for workpieces with a thickness of less than 20mm. The device includes the upper part of the forced cooling device and the lower part of the forced cooling device. The sealing gasket is installed at the upper and lower parts of the forced cooling device, and the upper and lower parts of the forced cooling device are integrally formed; wherein, the upper part of the forced cooling device includes an upper body and a heat dissipation structure located at the bottom center of the upper body, and a workpiece matching the size of the workpiece is set in the center of the upper body. Groove, the depth of the workpiece groove is less than the thickness of the upper body, the upper body is uniformly provided with threaded holes for mounting the pressure plate, the workpiece is fixed through the pressure plate, and the upper body is also uniformly provided with threaded holes for connecting the lower part of the forced cooling device; The center of the upper surface of the lower part of the forced cooling device is provided with a cooling water channel that matches the size of the heat dissipation structure. The two ends of the cooling water channel and the two sides of the lower part of the forced cooling device are respectively equipped with a cooling water channel inlet and a cooling water channel outlet. The lower part of the forced cooling device The upper surface is also uniformly provided with bolt holes for connecting the upper body.

The heat dissipation structure is composed of a plurality of heat dissipation fins arranged at equal intervals.

Features and beneficial effects of the present invention: Compared with liquid argon spray cooling, the device of the present invention is easier to assemble, has higher operational safety, lower maintenance cost, and cooling from the bottom of the workpiece is conducive to the vertical extension of directional solidified tissue growth; compared with liquid nitrogen cooling, the present invention does not cause a drastic cooling effect on the workpiece as a whole, thereby inhibiting the formation of directional solidified structures. Through the experimental test using the device of the present invention, the directionality of the directional solidified tissue in the laser cladding layer is better and the volume fraction is larger, achieving the effect of optimized growth of the directional solidified tissue, ensuring the consistency of the repaired tissue and the original tissue of the workpiece, and the repair effect better.

Description of drawings

Fig. 1 is the working principle diagram of existing laser deposition liquid argon cooling device;

Figure 2 is a schematic diagram of the existing laser cladding liquid nitrogen cooling device;

Fig. 3 is a schematic diagram of the working principle of the forced cooling device of the present invention;

Fig. 4 is the plan view of forced cooling device top of the present invention;

Fig. 5 is the A-A sectional view of forced cooling device top of the present invention;

Fig. 6 is the B-B sectional view of forced cooling device top of the present invention;

Fig. 7 is the plan view of the lower part of the forced cooling device of the present invention;

Fig. 8 is the A-A sectional view of forced cooling device bottom of the present invention;

Fig. 9 is the B-B sectional view of forced cooling device bottom of the present invention;

Fig. 10 (a) is the structure diagram of the cladding layer obtained by using the forced cooling device of the present invention to carry out the laser cladding experiment;

Fig. 10(b) is a structure diagram of the cladding layer obtained from a laser cladding experiment without using the forced cooling device of the present invention.

detailed description

Because in the laser cladding process of directionally solidified alloys, increasing the temperature gradient of the solidification interface is conducive to the formation of a larger proportion of columnar grain structure. Therefore, the present invention considers adding a forced cooling device at the bottom of the workpiece to increase the temperature gradient from bottom to top during the cladding process, so that the direction of the formed directional solidification structure can be consistent and the volume fraction is larger.

A kind of forced cooling device for laser cladding directionally solidified alloy proposed by the present invention is described in detail below in conjunction with the accompanying drawings and specific examples:

The present invention proposes a forced cooling device for laser cladding directionally solidified alloys, the overall structure of which is shown in Figure 3, and the present invention is suitable for workpieces with a thickness t<20mm. This device includes the upper part of the forced cooling device and the lower part of the forced cooling device. The upper and lower parts are connected by threads, and a gasket is installed at the joint. The sectional view and the B-B sectional view are shown in Figures 4, 5, and 6 respectively, including the upper body 1 and the heat dissipation structure 3 located at the bottom center of the upper body 1, and a workpiece groove 2 matching the size of the workpiece 12 is set in the center of the upper body 1. The workpiece The depth of the groove 2 is smaller than the thickness of the upper body 1, and the upper body 1 is evenly provided with threaded holes 4 for mounting the pressure plate, through which the workpiece 12 is fixed and the workpiece is prevented from warping during the laser cladding process, and the upper body 1 is also uniform There is a threaded hole 5 for connecting the lower part of the forced cooling device; the top view, A-A sectional view, and B-B sectional view of the forced cooling device lower part 6 are shown in Figures 7, 8, and 9 respectively. A cooling water channel 7 with matching dimensions, the two ends of the cooling water channel and the two side walls of the lower part 6 of the forced cooling device are respectively provided with a cooling water channel inlet 8-1 and a cooling water channel outlet 8-2, and the upper surface of the lower part 6 of the forced cooling device Bolt holes 5 for connecting the upper body 1 are evenly provided.

The specific implementation mode and function of each component of the present invention are described in detail as follows:

Before laser cladding, the workpiece 12 is clamped in the workpiece groove 2. Since heat conduction is the main heat transfer mode during the cooling process, the upper part of the forced cooling device needs to be made of metal with good thermal conductivity, such as silver, copper, gold and aluminum. Silver has the best thermal conductivity among metals, but it is expensive and difficult to process. The preferred copper is high-purity copper. The thermal conductivity is slightly inferior to silver but better than gold and aluminum, and the price is moderate. In this embodiment, copper is used to make the forced cooling device Upper part; the threaded hole 4 used to install the pressure plate in the upper part of the forced cooling device has no specific restrictions, and the appropriate size can be selected according to the shape of the workpiece and the clamping requirements, but the depth cannot exceed the thickness of the upper body 1; the threaded hole 5 in the upper part of the forced cooling device has no specific restrictions Restrictions are used to connect the upper and lower parts of the forced cooling device, but the position must not interfere with the heat dissipation structure 3. The workpiece 12 of the present embodiment is a rectangular plate structure, the length of the workpiece is 1 mm, the width is w mm, the thickness is t mm, the length of the forced cooling device top is (1+40) mm, and the width is (w × 2 +30)mm, height is (t+7)mm, length of workpiece groove 2 is (l+1)mm, width is (w+1)mm, depth is (t-1)mm, bottom surface of workpiece groove 2 to The distance between the top surfaces of the heat dissipation structure 3 is 8mm.

The heat dissipation structure 3 is composed of a plurality of heat dissipation fins arranged at equal intervals. During operation, the heat dissipation fins are inserted into the cooling water channel 7 of the lower part 6 of the forced cooling device. ) contact and convective heat transfer are the main heat transfer methods, so increasing the surface area of each heat sink is conducive to heat transfer. Specifically, the size of the heat sink can be selected according to the design method of the profile heat sink in the "Electronic Radiator Technical Manual"; The length of the heat dissipation structure 3 of the embodiment is equal to the length 1 of the workpiece, and the width is (w×2-3) mm. The thickness of a single heat sink is 3 mm, and the height is 24 mm. The clear distance between two adjacent heat sinks is 3 mm. The number of slices is an integer of w/3 and arranged symmetrically along the center of the workpiece groove.

The main function of the lower part 6 of the forced cooling device is to provide a cooling water channel matched with the heat dissipation structure, and conduct the cooling water. Metals with low price, good thermal conductivity and not easy to rust can be selected, such as: aluminum alloy and Stainless steel, aluminum alloy is used in this embodiment to make the lower part of the forced cooling device; the cooling water channel 7 is located at the center of the lower part 6 of the forced cooling device; Channel 7 is arranged in the lengthwise direction and is respectively located at the center of both ends of the cooling water channel. The inlet and outlet (8-1 and 8-2) of the cooling water channel are equipped with Green connectors for connecting the external cooling water inlet and outlet pipes (9 , 10); the position and size of the threaded hole 5 at the bottom of the forced cooling device and the threaded hole 5 at the top of the cooling device need to be strictly consistent. The length and width of the lower part 6 of the forced cooling device of this embodiment are equal to the length and width of the upper part of the forced cooling device respectively, and the height of the lower part of the forced cooling device is 30 mm; the length, width and depth of the cooling water channel of the present embodiment are respectively (l+ 10)mm, (w×2+3)mm, 25mm, the inlet and outlet of the cooling water channel are threaded holes with 4 points in imperial system.

The installation and cooling process of device of the present invention are:

Insert the upper heat dissipation structure 3 of the forced cooling device into the lower cooling water channel 7 of the forced cooling device, the upper and lower parts are connected through the threaded hole 5, and a gasket is installed at the junction; the inlet and outlet of the cooling water channel (8-1 and 8-2) Assemble the green connector and connect with the water pipe.

Before laser cladding, put the workpiece 12 into the workpiece groove 2, install the pressure plate through the threaded hole 4 to fix the workpiece, the cooling water flows into the cooling water channel inlet 8-1 from the cooling water inlet pipe 9, and flows through the cooling water channel 7, the cooling water and the cooling water The heat dissipation structure 3 in the water channel takes away the heat of the heat dissipation structure after full contact, and flows out from the cooling outlet pipe 10 through the outlet 8-2 of the cooling water channel. After ensuring that the cooling water continues to flow in and out, turn on the laser 11 for laser cladding. And the cooling water is continuously turned on during the whole laser cladding process. After the laser cladding is completed, the cooling water is stopped and the clamp is removed.

Using the forced cooling device of the present invention to carry out laser cladding experiments, the cladding layer structure is obtained as shown in Figure 10(a). Compared with the cladding layer structure without using the forced cooling device of the present invention in Figure 10(b), the orientation of the present invention is The proportion of columnar grain structure grown by solidification increases significantly, and the direction is consistent vertically upward.

The manufacturing cost of the forced cooling device of the present invention is relatively low, can effectively improve the forming quality of directionally solidified alloy columnar crystals in practical applications, and is a device that can effectively improve the temperature gradient of the solidification front during the laser cladding process of directionally solidified alloys.

Claims (5)

1. A forced cooling device for laser cladding directionally solidified alloys. This device is suitable for workpieces with a thickness less than 20mm. It is characterized in that the device includes the upper part of the forced cooling device and the lower part of the forced cooling device. The upper and lower parts pass through Threaded connection, a gasket is installed at the joint, and the upper and lower parts of the forced cooling device are integrally formed; wherein, the upper part of the forced cooling device includes an upper body (1) and a heat dissipation structure (3) located at the bottom center of the upper body. A workpiece groove (2) matching the size of the workpiece (12) is provided in the center of the main body. The depth of the workpiece groove is smaller than the thickness of the upper body, and the upper body is uniformly provided with threaded holes (4) for mounting the pressure plate, and the workpiece is fixed through the pressure plate. The upper body is evenly provided with threaded holes (5) for connecting the lower part of the forced cooling device; the center of the upper surface of the lower part (6) of the forced cooling device is provided with a cooling water channel (7) matching the size of the heat dissipation structure. The cooling water channel inlet (8-1) and the cooling water channel outlet (8-2) are respectively provided on both sides of the channel to the lower part of the forced cooling device, and the upper surface of the lower part of the forced cooling device is evenly provided with bolt holes connecting the upper body (5). 2 . The forced cooling device for laser cladding directionally solidified alloys according to claim 1 , wherein the heat dissipation structure is composed of a plurality of heat dissipation fins arranged at equal intervals. 3. The forced cooling device for laser cladding directionally solidified alloys according to claim 1, characterized in that, the inside of the cooling water channel inlet and the cooling water channel outlet are equipped with green holes for connecting the external cooling water inlet and outlet pipes. connector. 4. The forced cooling device for laser cladding directionally solidified alloy according to claim 1, characterized in that, the upper part of the forced cooling device is made of any one of silver, copper, gold or aluminum. 5. The forced cooling device for laser cladding directionally solidified alloys according to claim 1, wherein the lower part of the forced cooling device is made of aluminum alloy or stainless steel.